This invention relates to methods of and compositions for treating vascular defects, such as aneurysms and atriovenous malformations, and in particular a method and related apparatus for treating such defects with magnetically manipulated objects and materials.
There are many types of vascular defects that can be treated by blocking the defect. One example of such a defect is an aneurysm, which is a permanent, abnormal blood-filled dilatation or ballooning of a blood vessel that may be congenital or the result of disease. Aneurysms typically have thin walls vulnerable to rupture. If an aneurysm ruptures, the resulting hemorrhage that can put injurious pressure on surrounding tissue, impair downstream blood flow, and even cause death. Another example of a vascular defect is an atriovenous malformationxe2x80x94a typically congenital shunt formed between an artery and a vein that often carries a substantial blood flow. One of the principal complications in treating these and other vascular defects is the blood flow in the adjacent vessels which impairs treatment, but should be maintained for the health of the patient.
Current treatments for aneurysms include embolizing the aneurysm to remove the dilatation or balloon from the wall of the vessel. In the most mature technique, the surgeon accesses the region of the aneurysm under direct visualization and places one or more aneurysm clips on the opening or xe2x80x9cneckxe2x80x9d of the aneurysm. While this conventional surgical technique has a high rate of success, it is highly invasive and for that reason it is undesirable. More recently, less invasive techniques have been developed for the treatment of aneurysms. One such technique involves the introduction of small wire coils into the aneurysm. A catheter is navigated to the site of the aneurysm, and the coils are delivered through the lumen of the catheter into the aneurysm. The coils reduce the blood flow through the aneurysm, which results in clotting within the aneurysm. This coiling procedure can be time consuming both in navigating the catheter through the vasculature to the site of the aneurysm, and in introducing the coils into the aneurysm. In some cases, the shape of the aneurysm allows the coils to escape from the aneurysm, requiring the coil to be retrieved and replaced.
Another less invasive technique for treating vascular defects is the delivery of embolic materials to the site of the vascular defect to occlude the defect. In the case of an aneurysm a balloon is inflated over the neck of the aneurysm and a liquid embolic agent is introduced into the aneurysm. Attempts have been made to deliver embolic agents directly into the dilation or balloon of the aneurysm. Embolic agents have also been used to occlude atriovenous malformations, but it can be difficult to accurately deliver the embolic agents. In one of the more common procedures a catheter is navigated to the site of the atriovenous malformation and particles of polyvinyl alcohol with sizes selected for the particular application are introduced. This procedure requires guessing at the proper size of the particles and there is limited control over the placement of the particles, which upon release follow the path of greatest flow.
Alksne, xe2x80x9cIron-acrylic Compound for Stereotactic Aneurysm Thrombosis.xe2x80x9d J. Neurosurg. 47:137-141 (1977), incorporated herein by references, discloses injecting an iron-acrylic mixture into the dome of an aneurysm, and holding the mixture in place with a magnet inside the body. Gaston et al., xe2x80x9cExternal Magnetic Guidance of Endovascular Catheters with Superconducting Magnet: Preliminary Trialsxe2x80x9d J. Neuroradiol. 15: 137-147 (1988), incorporated herein by reference, discloses delivering magnetic particles with an external source magnet. Evans, U.S. Pat. No. 5,702,361 xe2x80x9cMethod of Embolizing blood Vesselsxe2x80x9d incorporated herein by reference, discloses various embolizing agents including polymers and/or adhesives. Granov et al., U.S. Pat. No. 5,236,410, xe2x80x9cTumor Treatment Method,xe2x80x9d incorporated herein by reference, discloses the use of magnetic materials in tumor treatment.
Difficulties with prior embolic agents include complications from the delivery method, which sometimes employed balloons to temporarily block flow through the vessel and the difficulty in controlling and containing the embolic agents, which allows some material to escape and block downstream vessels.
In addition, some embolic agents did not adequately adhere to the vessel walls, allowing blood to seep between the embolic plug and the vessel wall. When biocompatible adhesives were used, the adhesives tended to adhere to the delivery equipment, resulting in a potentially fatal attachment of the delivery catheter to the embolic plug, or the pulling of a xe2x80x9cstringxe2x80x9d of embolic material from the body of embolic material as the delivery catheter was retracted.
Another limitation on the use of embolic agents has been the limited ability to simultaneously view the ejection of the embolic agent under fluoroscopy of adequate quality. Conventional image intensifiers cannot operate in the presence of magnetic fields much larger than the relatively weak field of the earth (about 0.5 gauss). Fields of hundreds to thousands of gauss are required to control magnetic embolic agents, and these fields must be projected at distances large enough to reach aneurysms inside the body. External magnets which project such strong fields prohibit the use of conventional image intensifiers near the patient. One attempted solution is to use mirrors to project the X-ray image impinging on a phosphor plate to a remote camera, but this approach is not practical for human operating room procedures. First, the loss of light intensity due to the optical converter would require increased X-ray intensity which is unacceptable in clinical hospital settings. Second, the dim light being projected would require that the optical path to the distant camera be entirely black. This is difficult to implement with moving imaging systems.
Despite these and other possible difficulties, flowable embolic agents offer advantages over objects including the ability to uniformly fill the defect, and the relative ease of delivering a flowable embolic agent versus multiple discrete objects, such as coils.
The present invention provides improved methods and related devices for treating vascular defects. According to one aspect of this invention, various magnetic objects are provided that can be delivered intravascularly through a catheter and which can be guided into and/or held in place in the vascular defect with an applied magnetic field. One embodiment of these magnetic objects includes magnetic coils. These coils may either be magnetic, or include magnetic elements. Another embodiment of these magnetic objects includes a magnetic patch, adapted to cover the vascular defect. The magnetic patch may include a hoop for ensuring that the patch is fully deployed.
In another aspect of this invention, a catheter is provided for delivering the magnetic objects and materials of the present invention. The catheter has a proximal end and a distal end, and lumen therebetween. There is a coil at the distal end, and leads extending along the catheter by which a current can be selectively applied to the coil at the distal end 126 of the catheter. Current can be selectively applied to the coil on the distal end of the catheter to selectively enhance the magnetic responsiveness of the distal end of the catheter so that it can be navigated in the body with an externally applied magnetic field, but the coil can be disconnected from current so that the coil does not interfere with the delivery of magnetic objects or magnetic materials through the lumen. The magnetism created by the current in the coil is enhanced by the presence of the magnetic objects or the magnetic material in the lumen of the catheter. The coil can also be energized to help retain magnetic materials in the lumen of the catheter. A second coil may be provided on the catheter to enhance magnetic responsive and to enhance the ability to retain magnetic materials in the lumen. In another embodiment, lateral coils (as opposed to circumferential coils) are provided in the sidewall of the catheter. These coils facilitate movement of the distal end 126 of the catheter, for example when it is n the opening of an aneurysm.
Thus, the method and devices of the present invention allows a catheter to be brought to the procedure site through magnetically assisted navigation, but the catheter can remain at the site as a further magnetic procedure, such as the magnetic delivery of magnetic objects and magnetic materials, is conducted.
In accordance with one aspect of this invention a liquid embolic agent is provided with a magnetic constituent, which allows the magnetic embolic agent to be controlled by a magnetic field applied by an external source magnet. The applied magnetic field creates a force that draws the magnetic embolic agent into the defect completely filling the defect without voids. The force direction can be adjusted during the procedure by moving an external magnet or changing the direction of externally generated fields to optimize filling. The magnetic force obviates the need for an occluding balloon, allowing more distal sites to be treated with the catheter alone. Aneurysms of all shapes and at all locations can be treated equally by simply adjusting the magnetic force direction.
The magnetic embolic agent in accordance with another aspect of the present invention preferably combines a precipitating polymer and a glue. The precipitating polymer preferably comprises a biocompatible polymer chosen from the group comprising: cellulose acetate, polymethylmethacrylate, polyvinyl acetate, polyvinyl alcohol, hydrogel, polyurethane, polyethylene vinyl alcohol, or preferably cellulose acetate, and a biocompatible solvent chosen from the group comprising: dimethylsulfoxylate, ethyl alcohol, ethyl acetate, and preferably acetone. The solvent dissolves the polymer, and with the proper combination of viscosity and surface tension, the solution will then be able to homogeneously suspend paramagnetic particles. The solution is easy to deliver through a catheter to the vascular defect. The polymer precipitates at the vascular defect as the solvent dissipates into the blood. However, the polymer may not adhere to the walls of the vasculature, and may tend to internally fracture due to the lack of intra-polymer cohesion. Thus, an adhesive is preferably included to provide adhesion and cohesion. This adhesive is preferably either cyanoacrylate and fibrin glue. The adhesive stays inert in the polymer solution. However, once the magnetic material is ejected, the water activates the adhesive, the composition adheres to the vessel, and enhances the cohesiveness of the material as well. The weakened vessel wall is reinforced by the adhesive bond with the magnetic embolic material which fills the defect.
A metal powder such as barium or tantalum may be added to render the composition radiopaque and thus visible under fluoroscopy. Preferably the metal powder is paramagnetic material, i.e., one that is attracted by a magnetic field, but does not retain magnetism once the magnetic field is removed. The presence of the paramagnet particles allows the embolic composition to be directed, deposited, and held in place with a magnetic field. The paramagnetic particle is preferably a magnetic powder such as pure iron, carbonyl iron, coated iron and coated carbonyl iron (preferably pure iron) is used for both radiopacity and magnetic attraction.
The magnetic embolic material in accordance with the present invention allow magnetic control for superior placement. In some embodiments the settings of the material can be controlled buy the application of a curing agent. The embolic compositions have superior adhesion and cohesion. In one embodiment, the material becomes less magnetically responsive over time so that the embolic does not interfere with or restrict subsequent magnetic procedures such as magnetic surgical procedures or MRIs.